Chronic levels of intestinal tissue inflammation in IBD are associated with increased crypt cell apoptosis and an increased risk for development of colorectal cancer. Our results implicate p53 activation as a key step in mediating crypt cell apoptosis in states of intestinal inflammation. The primary role of p53 is to protect developing cell by repairing DNA damage and/or inducing apoptosis. The importance of p53 in the intestine is highlighted by observations that p53 mutations are detected early in patients with chronic UC (even before dysplasia), whereas in sporadic forms of colon cancer, p53 mutations occur relatively late. Specifically, 70% of UC-associated cancers and 20% of dysplastic lesions analyzed in UC contain p53 mutations. These clinical observations increase the importance of discovering mechanisms for p53 induction and activation during tissue inflammation. Studies in the present aim will utilize the anti-CD3 mAb-treated mouse model of T cell-induced crypt cell apoptosis. Based on preliminary results, we hypothesize that epithelial TNF receptor 1 and 2 signaling in epithelial cells induce epithelial p53 expression whereas TNF-induced iNOS expression in BM-derived cells releases NO that activates p53 protein and induces expression of downstream p53 target genes involved in crypt cell apoptosis. The elements of this pathway will be explored in the current proposal. First we will examine the cellular and molecular pathways involved in TNF receptor signaling and iNOS induction during Tcell-induced activation of p53. These studies will restrict expression of TNFR-1, TNFR-2 and iNOS to epithelial Vs BM-derived cells and examine p53 activation, expression of p53 targets and induction of crypt cell apoptosis. Next we plan to examine the downstream effectors of p53. We will use specific gene knockout mice (bax/bak and bid-/-) to address hypotheses based on analysis of p53 target genes in wild type and p53 null mice. Our previous studies significantly advanced out understanding of the critical steps in T cell-induced crypt cell apoptosis, yet there are key questions that remain unanswered. The current proposal will move us closer to understanding the cellular and molecular events required for the induction of crypt cell apoptosis in intestinal inflammation. These studies will enhance out understanding of the mechanisms relevant to normal crypt cell death and add insight into the pathways involved in the induction of intestinal carcinogenesis in IBD.